Miniaturized rotary potentiometers



May 12, 1970 w. D. KIRKENDALL MINIATURIZED ROTARY POT ENTIOMETERS 3 Sheets-Sheet 1 Filed June 28, 1968 a a a a m INVENTOR. W/zunm L? Mere/van ATTORNEYS May 12, 1970 w. D. KIRKENDALL 1 MINIATURIZED ROTARY POTENTIOMETERS Filed June 28; 1968 I 3 Sheets-Sheet z INVENTOR.

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INVENTOR. WILL/HM 0 K/RKENDALL ATTORNEYS United States Patent 3,512,113 MINIATURIZED ROTARY POTENTIOMETERS William D. Kirkendall, Dalton, Pa., assignor to Weston- Instruments, Inc., Newark, N.J., a corporation of Delaware Filed June 28, 1968, Ser. No. 741,053 Int. Cl. H01c /02 US. Cl. 338-163 9 Claims ABSTRACT OF THE DISCLOSURE Rotary potentiometers, particularly when miniaturized, wherein the housing comprises a cup-shaped member and a second member which serves both as a closure and as an adjusting knob, the cup-shaped member having a cylindrical side wall with an inwardly opening transverse annular groove, the second member including an initially cylindrical skirt having a transverse annular outwardly projecting ridge. Both housing members are formed of resiliently deformable, low-friction polymeric material and the relative dimensions are such that, when the second member is forced axially into the cup-shaped member, the skirt is deformed frusto-conically and the ridge is resiliently biased into engagement in the groove to retain the second member in a predetermined axial position while allowing the same to be rotated to adjust the potentiometer.

This invention relates to potentiometers of the type in which a rotary contact is adjustable along an arcuately extending resistance element. While more generally applicable, the invention is particularly advantageous when applied to miniaturized circular potentiometers.

Potentiometers of the type referred to conventionally employ an insulating housing comprising parts which are fitted together to define a closed cavity in which the rotary contact and the resistance element are disposed. The rotary contact must be adjusted from outside of the housing, and it has been found desirable to employ a portion of the housing structure as an adjusting member or knob which either directly carries the movable contact or is connected thereto. Though numerous devices of this type have been developed by prior-art workers, there is still an active demand for a structure which is simpler, yet more effective, than those heretofore adopted.

It is accordingly a general object of the invention to devise a rotary potentiometer of the type described wherein the housing can be made up of two members which are easily and simply interengaged in such fashion that one member can serve both as a closure for the housing and as the rotatable adjusting knob, no additional bearing or seal members being required.

Another object is to provide a miniaturized rotary potentiometer wherein a combination closure and adjusting member can be installed simply by axial insertion into a generally cupshaped housing member, the cup-shaped member and the closure and adjusting member directly engaging each other to afford the bearing and sealing features required.

Stated broadly, potentiometers according to the invention include two housing members fabricated from a resiliently deformable low-friction polymeric material, advantageously glass fiber-filled nylon, one member being cup-shaped and having a circularly extending side wall provided with a transverse annular inwardly opening groove, the other member being in the nature of a rotatable closure for the cup-shaped member and including an initially cylindrical skirt having an outwardly projecting transverse annular ridge, the groove and ridge having transverse cross-sectional configurations such that the ridge can mate with the groove, and the relative dimensions of the side wall of the cup-shaped member and the skirt, when the latter is in its relaxed, undeformed condition, being such that the skirt is deformed frusto-conically when the closure member is forced into the cup-shaped member, such deformation biasing the ridge into engagement in the groove in such fashion that the closure i retained in a predetermined axial position, yet is free to be rotated, for adjustment of the potentiometer, with the interengaged ridge and groove serving as a plain bearing.

In order that the manner in which the foregoing and other objects are attained in accordance with the invention can be understood in detail, particularly advantageous embodiments thereof will be described with reference to the accompanying drawings, which form a part of the original disclosure of this application, and wherein:

FIG. 1 is a longitudinal sectional view of a potentiometer constructed in accordance with one embodiment of the invention;

FIG. 2 is a view partly in plan elevation and partly in transverse cross section, taken generally on line 2-2, FIG. 1;

FIG. 3 is an axial cross-sectional view of a combined closure and adjusting knob forming part of the potentiometer of FIG. 1;

FIG. 4 is a sectional view similar to FIG. 1 illustrating a potentiometer constructed according to another embodiment of the invention;

FIG. 5 is a view partly in plan elevation and partly in transverse cross section, taken generally on line 55. FIG. 4; and

FIG. 6 is a fragmentary sectional view illustrating a modified form of a portion of devices of FIGS. 1 and 4.

In the embodiment of the invention shown in FIGS. 1-3, the housing of the potentiometer comprises a generally cup-shaped member 1 and a combined closure and adjusting knob 2. Member 1 is formed as an integral piece of a suitable polymeric material, advantageously glass fiber-filled nylon, having good electrical insulating and low-friction bearing characteristics, and includes a base or end wall 3 and a cylindrical side wall 4. Side wall 4 has a right cylindrical outer surface 5 and an inner surface, the latter being made up of two right cylindrical portions 6 and 7. Portion 6 is of smaller diameter and portion 7 of larger diameter, the two portions being joined by a transverse annular shoulder 8 which faces away from end wall 3, that is, toward the open end 9 of side wall 4.

Adjacent end wall 3, surface portion 6 is interrupted by a projection 10 which extends generally radially inwardly. Adjacent shoulder 8, surface portion 6 is interrupted by a transverse annular inwardly opening groove 11 of triangular transverse cross section. Surface portion 7 is interrupted by a generally radially inwardly projecting abutment 12.

The inner face 13 of end wall 3 is recessed at 14 to accommodate a thin conductive metal strip 15 to which a terminal pin 16, which extends through and projects outwardly from wall 3, is electrically and mechanically connected. A wire wound resistance element 17, which is of circular transverse cross section and extends arcuately for slightly less than 360, is secured within member 1. The resistance element extends in continuous engagement with surface portion 6 and face 13 and is so disposed that projection 10 extends between the ends of the resistance element, so that the latter is positively located rotationally with respect to member 1. Two additional terminal pins 18 extend through wall 3 and project outwardly therefrom, and two lead wires 19 are provided, each soldered to a different one of pins 18 and a different one of the ends of resistance element 17.

Combined closure and adjusting knob 2 is also made as in integral piece from glass fiber-filled nylon or other synthetic polymeric material having good electrical insulating and low-friction bearing characteristics. As best seen in FIG. 3, member 2 includes a cylindrical portion 20 having an outwardly projecting, integrally formed stop element 21. One end face 22 of member 2 has a diameter only very slightly smaller than the diameter of inner surface portion 7 of side wall 4. The diameter of portion 20, discounting stop element 21, is less than the diameter of surface portion 7 by the radial dimension of abutment 12. To provide the larger diameter for end face 22, a thin transverse circularly extending flange 23 is provided.

The overall thickness or axial dimension of the combined closure and adjusting knob 2 is substantially greater than that of portion 20, the balance of member 2 being in the form of a thin annular skirt 24 and a second cylindrical portion 25. Before member 2 is installed, the skirt 24 is in a normal undistorted condition and is cylindrical its inner surface 26 being a right cylindrical surface and its outer surface 27 being right cylindrical and provided with an outwardly projecting transverse annular rib or ridge 28. The diameter of outer surface 27 is only slightly smaller than that of inner surface portion 6, and the skirt joins portion 20 at a transverse annular shoulder 20. The radial height of ridge 28 is markedly greater than the depth of groove 11 and therefore, large as compared to the difference between the radius of curvature of cylindrical surface portion 7 and the radius of curvature of surface 27. Skirt 24 and cylindrical portion 25 can be considered as projecting axially from the end of portion 20 which is Opposite from face 22, and shoulder 29 faces in the same direction as skirt 24 and portion 25 project.

Within skirt 24, when the skirt is in the normal or undistorted condition seen in FIG. 3, is an annular space defined by the inner surface 26 of the skirt and the right cylindrical outer surface 30 of portion 25, the radical width of this space being significantly larger than the difference between the height of ridge 28 and the depth of groove 11.

The centrally disposed portion 25 of member 2 is provided with a recess 31 which is generally in the form of an elongated rectangle with the long dimension of the rectangle extending diametrically with respect to cylindrical portion 25, the recess opening at one end through the periphery of portion 25. The bottom wall of recess 31 is provided with a cylindrical boss 32, centered on the axis of cylindrical portion 20, and two elongated, straight-sided, parallel bosses 33 located each on a different side of boss 32 and spaced equally therefrom. The movable contact member 34 is made from an integral piece of spring sheet metal and includes a flat rectangular base portion 35 having an aperture which accommodates boss 32, the two parallel straight sides of the base portion being engaged each with a different one of bosses 33, portion 35 lying in flush engagement with the bottom wall of recess 31.

A first contact arm 36 extends from one end of portion 35 and is bent at an angle relative to the plane of portion 35, so that the contact arm slants outwardly and away from member 2. Arm 36 terminates in a cup-shape contact tip 37 which is concave with respect to member 2. A second contact arm 38 extends from the other end of portion 35 and is bent out of the plane thereof, the bend 39 extending for substantially more than 90 so that the straight body portion 40 of arm 38 slants inwardly and away from member 2. Arm 38 terminates in a cup-shaped contact tip 41 which is concave with respect to member 2. When the resilient contact member 34 is in relaxed, undistorted position, the angle at which arm 38 extends is such that tip 41 lies to the left (as viewed in FIG. 1) of the central axis of member 2.

End face 22 of the combined closure and adjusting knob 2 is provided with a centrally located, diametrically extending, rectangular recess 42 to accept a screwdriver 4 or like turning tool, and is also interrupted by a raised portion 43 which is of triangular plan shape and arranged at one end of recess 42 so that the recess and rectangular portion combine to form an arrow lying in the plane defined by arms 36 and 38 and therefore indicating the rotational position of contact tip 37.

The potentiometer is assembled by forcing the combined closure and adjusting knob 2 axially into member 1 until ridge 28 snaps into groove 11. Since the relaxed diameter of ridge 28 is greater than can be accepted by surface portion 6 of side wall 4, skirt 24 is defromed into frusto-conical form, tapering inwardly and away from portion 20, as the skirt is forced into place. Further, the diameter of groove 11 is sufficiently small to prevent the skirt from returning to its right cylindrical shape. Accordingly, skirt 24 remains in an inwardly deformed frusto-conical shape, providing a spring force which maintains ridge 28 positively engaged in groove 11. From FIG. 1, it will be noted that the annular space between skirt 24 and portion 25 provides adequate freedom for deformation of the skirt during assembly.

The transverse cross sections of groove 11 and ridge 28 are similar triangles, so that the ridge and groove mate with approximate preciseness when the ridge snaps into the groove. Interengagement between groove 11 and ridge 28 serves to retain member 2 in a precisely predetermined axial position relative to member 1. With member 2 so positioned, the space between the bottom surface of recess 31 and surface 13 of end Wall 3 is less than would accommodate arm 38 in undistorted condition. Accordingly, as member 2 is forced into place, contact tips 37 and 41 come into sliding engagement with the resistance element and strip 15, respectively, and arms 36 and 38 are distorted resiliently toward member 2, so as to assure good engagement between contact tips 37, 41 and, respectively,-

resistance element 17 and strip 15.

In addition to retaining the combined closure and adjusting knob 2 in its predetermined axial position on member 1, engagement of ridge 28 in groove 11 provides a bearing means which assures that member 2 can be r0- tated at will to adjust the position of contact tip 37 on resistance element 17. The polymeric material from which members 1 and 2 are fabricated, affording low-friction bearing characteristics, assures that free rotation of memher 2 relative to member 1 can be accomplished at will, but the biasing force supplied by inwardly distorted skirt 24 to urge ridge 28 into groove 11 preloads the bearing constituted by the ridge and groove to such an extent that, save when a predetermined turning force is applied to member 2, the member 2 is held in that rotational position to which it has been adjusted.

Additionally, since groove 11 and ridge 28 are both continuous and unbroken, engagement of the ridge in the groove, maintained under pressure because of the inwardly distorted condition of skirt 24, provides an effective seal against entry of foreign matter into the cavity occupied by the resistance element and contact member. In this connection, it is also to be noted that, though there is necessarily a significant space between surface portion 7 and the cylindrical surface of portion 20 of member 2, except in the areas occupied by abutment 12 and stop element 21, that space is effectively closed by flange 23.

FIGS. 4 and 5 illustrate a potentiometer constructed in accordance with another embodiment of the invention. Here, the housing again includes cup-shaped member 51 and a combined closure and adjusting knob 52. Member 51 is substantially identical to member 1 except that the cylindrical side wall 54 is substantially thicker. In this embodiment the outer end portion of member 52 includes an outwardly projecting transverse circular flange 73 which overlies the adjacent end face of side wall 54 in the as sembled potentiometer, providing a knob portion which can be grasped between the thumb and forefinger. The relationship between skirt 74, with ridge 78, to member 52 and the side wall 54, with groove 61, remains as described with reference to FIGS. 13.

FIG. 6 illustrates a modified form of ridge and groove arrangement useful in the devices of FIGS. l-S. Here, the side wall 104 is identical to elements 4 and 54, hereinbefore described, save that the groove 111, while being of triangular transverse cross section, is disposed with that one of its walls which is most distant from the resistance element (not shown) lying in a plane at right angle to skirt 124. Similarly, the corresponding side of ridge 128, which is again of triangular cross section, extends at right angles to skirt 124. Accordingly, the engaged surfaces of the ridge and the groove are more nearly normal to the direction of any axially directed force tending to withdraw the combined closure and adjusting knob 102 from the cupshaped member 101, and the member 102 is thus especially securely retained.

It will be noted that, in all of the illustrated forms of the invention, the contact arms are resiliently deformed, once the potentiometer is assembled, in such a fashion as to urge the combined closure and adjusting knob away from the end or base wall of the cup-shaped main housing member. This action of the contact arms urges one side of the ridge into positive engagement with the corresponding side of the groove, assuring a smooth and uniform rotary bearing action.

Where reference has been made to miniaturized potentiometers, it will be understood by those skilled in the art that the diameter of the cup-shaped housing member can be significantly less than one-half inch.

What is claimed is:

1. In a rotary potentiometer, the combination of housing means defining a generally cup-shaped cavity having an end wall and a side wall, said side wall having a circularly extending inner surface provided with a transverse annular inwardly opening groove; a combined closure and adjusting knob including a cylindrical portion dimensioned to be embraced by the end of side wall opposite said end wall and a skirt integral with said cylindrical portion and projecting therefrom, said cylindrical portion and said skirt being of syntthetic polymeric material, said skirt having a transverse annular outwardly projecting ridge of a transverse cross-sectional size and shape to be slidably engaged in said groove, said skirt being cylindrical when in relaxed, undistorted condition and the diameter of said ridge then being slightly larger than the diameter of said groove, said skirt being sufliciently resiliently distortable to allow said combined closure member and adjusting knob to be forced axially into said open end of said side wall until said ridge is engaged in said groove, the differences between the diameters of said ridge and groove causing said skirt to assume a frusto-conical shape so that said ridge is urged into said groove as a result of resilient deformation of said skirt, said ridge and groove coacting to provide a bearing which rotatably supports said combined closure and adjusting knob on said side wall; an arcuate resistance element disposed within said cavity; and contact 6 means carried by said combined closure and adjusting knob and including a contact slidably engaging said resistance element.

2. The combination defined in claim 1, wherein said combined closure and adjusting knob is an integral member which includes said cylindrical portion and said skirt.

3. The combination defined in claim 2, wherein said side wall is relatively thicker in the loeaton occupied by said groove and includes a thinner end portion on the side of said groove opposite said end wall, a portion of said inner surface at said end portion being right cylindrical and of a diameter larger than that of the mouth of said groove, there being a transverse annular shoulder directed away from said end wall and joining said portion of said inner surface at said end portion of said side wall with the por tion of said inner surface containing said groove, said cylindrical portion of said combined closure and adjusting knob being embraced by said end portion of said side wall.

4. The combination defined in claim 3, wherein said combined closure and adjusting knob has an outer end face which intersects the peripheral surface of said cylindrical portion, and said combined closure and adjusting knob does not project beyond said end of said side wall.

5. The combination defined in claim 3, wherein said combined closure and adjusting knob includes an enlarged outer end portion which projects outwardly from said cylindrical portion and overlies said end of said side wall.

6. The combination defined in claim 3 wherein the peripheral surface of said cylindrical portion of said combined closure and adjusting knob is interrupted by a stop element which projects outwardly therefrom, and said portion of said inner surface at said end portion of said side wall is interrupted by an inwardly projecting abutment to cooperate with said stop element for limiting rotation of said combined closure and adjusting knob.

7. The combination defined in claim 2, wherein said combined closure and adjusting knob includes a second cylindrical portion spaced concentrically inwardly from said skirt and having an axial length approximating that of said skirt, said contact means being secured to said second cylindrical portion.

8. The combination defined in claim 1, wherein the surface of said ridge which faces said end wall slants inwardly and toward the free end of said skirt.

9. The combination defined in claim 8, wherein said ridge and said groove have mating triangular transverse cross sections.

References Cited UNITED STATES PATENTS THOMAS J. KOZMA, Primary Examiner U.S. Cl. X.R. 200-468; 220 

